How do i change a pump in a vokera mynute 20se?

You have to drain boiler system from drain out point ,or drain boiler only shut flow and return valves drain from pressure relive valve ,but first option is best ,no need change body of pump just undo four head screw and change head ,refit head fill system 1.2bar and bleed rads and pump the big silver nut in middle

ltd
November 2012